(1) Field of the Invention
The present invention relates to a method for polishing a semiconductor wafer or the like.
(2) Description of Related Art
In a polishing process for a semiconductor wafer or the like, an abrasive cloth is dressed using a dressing member during polishing to prevent the abrasive cloth from becoming clogged during polishing and keep the polishing rate constant. Abrasive diamond grains are typically embedded in a surface of the dressing member, and the abrasive cloth is dressed by cutting a surface of the abrasive cloth using the abrasive diamond grains.
With an increase in the time during which a dressing member is used, the ability of the dressing member to cut an abrasive cloth decreases due to the dropping off or the like of abrasive diamond grains. In this case, clogging of the abrasive cloth is not eliminated, resulting in the reduced polishing rate of a semiconductor wafer.
In a polishing process for a semiconductor wafer, it is very difficult to measure the amount of the semiconductor wafer polished during polishing. Therefore, a semiconductor wafer is typically polished using, as an index, the polishing time determined based on the target amount of the semiconductor wafer polished and the polishing rate. It is thus very significant to keep the polishing rate of the semiconductor wafer constant, and one dressing member need be appropriately replaced in a polishing process for a semiconductor wafer.
An interval at which a dressing member is replaced is set based on previously obtained correlation data between the time during which the dressing member is used or the number of processed semiconductor wafers and a process result, such as the polishing rate. A dressing member is replaced at the time when a process abnormality, such as the reduced polishing rate, is detected by periodically checking a wafer to be monitored.
On the other hand, attempts have been made to keep the amount of a semiconductor wafer polished constant by resetting the polishing time in accordance with reduction in the polishing rate. A method in which reduction in the polishing rate is estimated by monitoring the torque of a motor for rotating an abrasive cloth and the polishing time is accordingly reset to keep a predetermined amount of the semiconductor wafer polished is disclosed in, for example, Japanese Unexamined Patent Publication No. 2002-103202.
In this known method, when a dressing member is replaced on condition that the time during which a dressing member is used is fixed, an apparent life of a dressing member becomes shorter than an actual life thereof so that a still available dressing member is replaced. The reason for this is that dressing members themselves have individually different lives. Furthermore, when dressing members having a short life are used, one of the dressing members is replaced after a wafer to be monitored are checked for reduction in the polishing rate. As a result, the deterioration of the dressing member cannot be found until the wafer to be monitored is checked. Since the deterioration of the dressing member cannot therefore be previously sensed, an abnormally polished product might be produced.
In a method in which the polishing rate is estimated and the polishing time is varied according to the estimated polishing rate, the polishing time becomes long. Furthermore, in this case, the life of each dressing member is unspecified, and therefore the time at which the dressing member should be replaced cannot be determined.